Not Applicable.
1. Field of Invention
This invention relates to the field of tomography devices. More specifically, the present invention is related to a method for manufacturing a scintillator composition having a graded decay time for use in association with tomography devices.
2. Description of the Related Art
In the field of tomography, it is well known to use scintillators for collecting and attenuating data relative to a test subject. Scintillation crystals are known to be grown using the Czochralski technique. In performing tests with scintillator, and specifically with respect to scintillation decay time, it is known to use a pulse shape discrimination technique, absolute calibrated in a Bollinger-Thomas experiment. Each of these techniques is disclosed by Casey M E, Eriksson L, Schmand M, Andreaco M S, Paulus M, Dahlborn M, Nutt R, xe2x80x9cInvestigation of LSO crystals for high spatial resolution position emission tomography,xe2x80x9d IEEE Trans Nucl Sci, vol 44, 1109-1113, 1997.
It is further known to grow scintillator crystals from various compositions to achieve differing results. U.S. Pat. No. 5,660,627 issued to Manente et al., discloses a method for growing Lutetium Oxyorthosilicate (LSO) crystals. The ""627 method uses the Czochralski method and controls the rate of rotation and the diameter of the crystal to produce a crystal exhibiting less variability in scintillation behavior in order to make them suitable for spectroscopic uses.
C. L. Melcher, in U.S. Pat. No. 4,958,080 teaches the use of a Cerium-doped LSO (LSO:Ce) as a scintillator material.
The present invention is a method for manufacturing a Cerium-doped Lutetium Oxyorthosilicate (LSO:Ce) scintillator having a graded decay time. The method for manufacturing an LSO:Ce crystal boule having a decay time gradient decreasing from the top end to the bottom end first includes the step selecting an iridium crucible. The crucible is selected based upon its diameter relative to the diameter defined by said crystal boule. Alternatively, or additionally, the crucible is selected based upon its volume relative to the volume of the crystal boule to be grown. A Cerium dopant (CeO2) is added to a mixture of Lutetium Oxide (Lu2O3) and Silicon Dioxide (SiO2). The composition is heated until melted to define a melt. A seed crystal is then placed in contact with the melt, is rotated, and slowly withdrawn, thereby yielding an LSO:Ce crystal boule defining a decay time gradient.